Methods for initiating operating voltages for subscriber identity cards and systems utilizing the same

ABSTRACT

A system for operating at least two subscriber identity cards has a subscriber identity module (SIM) controller generating a first voltage variable signal with a first voltage level to a first subscriber identity card during a first time period, generating the first voltage variable signal at a second voltage level to the first subscriber identity card during a second time period, receiving a first code indicating that generated voltage matches from the first subscriber identity card during the first or second time period, generating a first operating voltage with the first voltage level to the first subscriber identity card when receiving the first code in the first time period, generating the first operating voltage with the second voltage level when receiving the first code in the second time period.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending application Ser. No.12/172,469, filed Jul. 14, 2008, which claims the benefit of U.S.Provisional Application No. 61/031,769, filed Feb. 27, 2008, theentirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for initiating a plurality ofsubscriber identity cards, and more particularly to a method forinitiating operating voltages of the subscriber identity cards in asystem.

2. Description of the Related Art

Currently, the Global System for Mobile communication (GSM) standard isthe popular standard for mobile phones in the world. The GSM standard,standardized by the European Telecommunication Standards Institute(ETSI) is a cellular network structure and a Time Division MultipleAccess (TDMA) system. For a carrier frequency, the TDMA system willdivide a frame into eight time slots, wherein each time slot is used totransmit a channel data for a subscriber. In addition, the GeneralPacket Radio Service (GPRS) technology is one of the availabletechnologies of a GSM network. The GPRS technology utilizes the unusedchannels in the GSM network to provide moderate speed data transmission.The Wideband Code Division Multiple Access (W-CDMA) is a widebandspread-spectrum mobile air interface that utilizes the direct-sequencespread spectrum method of asynchronous code division multiple access toachieve higher speeds and support more users compared to theimplementation of time division multiplexing (TDMA) used by 2G GSMnetworks. Time Division-Synchronous Code Division Multiple Access(TD-SCDMA) is another type of 3G mobile telecommunications standard.

A dual SIM mobile phone is a phone with two Subscriber Identity Modules(SIMs), which correspond to different numbers. The dual SIM mobile phoneallows a user to use two communication services without carrying twophones at the same time. For example, the same mobile phone may be usedfor business and private use with separate numbers and bills, thusproviding convenience to mobile phone users. Typically, a SIM controllerinstalled in the mobile phone drives two SIMs with a fixed voltagelevel. However, when the operating voltages of the installed SIM orUniversal SIM (USIM) cards are different or the operating voltages ofinstalled SIM/USIM cards are different from the driving voltage level,the (U)SIM cards malfunctions.

BRIEF SUMMARY OF THE INVENTION

Methods for initiating operating voltages of subscriber identity cardsand the systems utilizing the same are provided. An embodiment of such asystem comprises a first subscriber identity card, a second subscriberidentity card, an RF module, a controller and a Baseband unit. Thecontroller initiates a first operating voltage of the first subscriberidentity card and initiates a second operating voltage of the secondsubscriber identity respectively. The Baseband unit cooperates with thefirst subscriber identity card to camp on a first cell and cooperateswith the second subscriber identity card to camp on a second cell viathe RF module.

Furthermore, an embodiment of a method for initiating operating voltagesof a first subscriber identity card and a second subscriber identitycard of a mobile station is provided. The mobile station furthercomprises a Baseband unit and an RF module. The Baseband unit is coupledto the first subscriber identity card, and a voltage variable signal isprovided to the first subscriber identity card. A first code from thefirst subscriber identity card is received when the voltage variablesignal is provided to the first subscriber identity card. A firstoperating voltage corresponding to the first code is provided to thefirst subscriber identity card. After the first operating voltage isprovided, the Baseband unit is coupled to the second subscriber identitycard and the voltage variable signal is provided to the secondsubscriber identity card. A second code from the second subscriberidentity card is received when the voltage variable signal is providedto the second subscriber identity card. A second operating voltagecorresponding to the second code is provided to the second subscriberidentity card. The voltage variable signal is an analog signal with afirst voltage level during a first time period and a second voltagelevel during a second time period, a voltage level of the firstoperating voltage is equal to the first or second voltage level, and avoltage level of the second operating voltage is equal to the first orsecond voltage level.

Moreover, another embodiment of a method for initiating operatingvoltages of a first subscriber identity card and a second subscriberidentity card of a mobile station is provided. The mobile stationfurther comprises a Baseband unit, a controller and an RF module. Afirst signal from the Baseband unit is provided to the controller via afirst interface. A second interface of the Baseband unit is coupled tothe first subscriber identity card by the controller after the firstsignal is provided. A voltage variable signal is provided to the firstsubscriber identity card by a first regulator of the controller when thesecond interface of the Baseband unit is coupled to the first subscriberidentity card. A first code from the first subscriber identity card isreceived by the Baseband unit via the second interface when the voltagevariable signal is provided to the first subscriber identity card.Voltage level settings are performed to the first regulator and a firstlevel shifter according to the first code, wherein the first regulatorand the first level shifter are coupled to the first subscriber identitycard. A second signal from the Baseband unit is provided to thecontroller via the first interface after the voltage level settings ofthe first regulator and the first level shifter are completelyperformed. The second interface of the Baseband unit is coupled to thesecond subscriber identity card by the controller after the secondsignal is provided. The voltage variable signal is provided to thesecond subscriber identity card by a second regulator of the controllerwhen the second interface of the Baseband unit is coupled to the secondsubscriber identity card. A second code from the second subscriberidentity card is received by the Baseband unit via the second interfacewhen the voltage variable signal is provided to the second subscriberidentity card. Voltage level settings are performed to the secondregulator and a second level shifter according to the second code,wherein the second regulator and the second level shifter are coupled tothe second subscriber identity card. The voltage variable signal is ananalog signal with a first voltage level during a first time period anda second voltage level during a second time period, and a voltage levelof the first operating voltage is equal to the first or second voltagelevel, and a voltage level of the second operating voltage is equal tothe first or second voltage level.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows a mobile station according to an embodiment of theinvention;

FIG. 2 shows a schematic diagram of a mobile station according to anembodiment of the invention;

FIGS. 3A and 3B show an embodiment of a method for initiating operatingvoltages of subscriber identity cards in a mobile station; and

FIGS. 4A, 4B, 4C and 4D show the different waveforms of exemplaryvoltage variable signals.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

A subscriber identity module (SIM) card typically contains user accountinformation, an international mobile subscriber identity (IMSI) and aset of SIM application toolkit (SAT) commands and provides storage spacefor phone book contacts. A micro-processing unit (MCU) of the Basebandchip (simply referred to as a Baseband MCU hereinafter) may interactwith MCUs of the SIM cards (each simply referred to as a SIM MCUhereinafter) to fetch data or SAT commands from the plugged in SIMcards. A mobile station is immediately programmed after plugging in theSIM card. SIM cards may also be programmed to display custom menus forpersonalized services.

A universal SIM (USIM) card is inserted in a mobile station foruniversal mobile telecommunications system (UMTS) (also called 3G)telephony communication. The USIM card stores user account information,an IMSI, authentication information and a set of USIM ApplicationToolkit (USAT) commands and provides storage space for text messages andphone book contacts. A Baseband MCU may interact with a MCU of the USIMcard (each simply referred to as a USIM MCU hereinafter) to fetch dataor SAT commands from the plugged in USIM cards. The phone book on theUSIM card has been greatly enhanced when compared to the SIM card. Forauthentication purposes, the USIM card may store a long-term presharedsecret key K, which is shared with the Authentication Center (AuC) inthe network. The USIM MCU may verify a sequence number that must bewithin a range using a window mechanism to avoid replay attacks, and isin charge of generating the session keys CK and IK to be used in theconfidentiality and integrity algorithms of the KASUMI (also termedA5/3) block cipher in the UMTS. A mobile station is immediatelyprogrammed after plugging in the USIM card.

A removable User Identity Module (R-UIM) or a Code Division MultipleAccess (CDMA) Subscriber Identity Module (CSIM) card has been developedfor a CDMA mobile station and is equivalent to the GSM SIM and 3G USIMexcept that it is capable of working in CDMA networks. The R-UIM or theCSIM card is physically compatible with the GSM SIM card, and providessimilar security mechanisms for the CDMA system. The IMSI is a uniquenumber associated with a global system for mobile communication (GSM) ora universal mobile telecommunications system (UMTS) network user. TheIMSI may be sent by a mobile station to a GSM or UMTS network to acquireother details of the mobile user in the Home Location Register (HLR) oras locally copied in the Visitor Location Register (VLR). An IMSI istypically 15 digits long, but may be shorter (for example MTN SouthAfrica's IMSIs are 14 digits). The first 3 digits are the Mobile CountryCode (MCC), and are followed by the Mobile Network Code (MNC), either 2digits (European standard) or 3 digits (North American standard). Theremaining digits are the mobile subscriber identification number (MSIN)for a GSM or UMTS network user.

To reduce hardware costs, new mobile stations may be equipped with asingle radio frequency (RF) module and Baseband chip respectively, andtwo subscriber identity cards may be plugged into two sockets of eachmobile station connecting to the single Baseband chip, where eachsubscriber identity card is provided by a particular network operator.The subscriber identity card may be a SIM, USIM, R-UIM or CSIM card. Themobile station may therefore simultaneously camp on two cells providedby either the same network operator or different network operators forthe plugged in SIM cards and operate in stand-by modes using the singleRF module and Baseband chip. A dual SIM controller is coupled/connectedbetween the Baseband chip and two SIM/USIM cards and powered by a powermanagement integrated chip (PMIC) and a battery. The Baseband chip readsdata from one of the SIM/USIM cards and writes data to one of theSIM/USIM cards via the dual SIM controller. The dual SIM controllerpowers the SIM/USIM cards with the same or different voltage levelsaccording to requirements thereof, wherein the voltage level for eachSIM/USIM card is determined during initiation. In general, the operatingvoltage level in a SIM/USIM card may be 1.8V or 3V. In addition, thedual SIM controller selectively transfers the SIM/USIM clock, reset anddata signals to the SIM/USIM cards according to instructions issued bythe Baseband chip.

FIG. 1 shows a mobile station 100 according to an embodiment of theinvention. The mobile station 100 comprises a Baseband chip 110, an RFmodule (or transceiver) 120, a dual SIM controller 130, a powermanagement integrated chip (PMIC) 140, a battery 150 and two subscriberidentity cards 160 and 170. As described above, the dual SIM controller130 is coupled/connected between the Baseband chip 110 and thesubscriber identity cards 160 and 170, and the dual SIM controller 130is powered by the PMIC 140 and the battery 150. In the mobile station100, the Baseband chip 110 may camp on a first cell corresponding to thesubscriber identity card 160 and a second cell corresponding to thesubscriber identity card 170 via the RF module 120, wherein the firstand second cells may been provided by either the same network operatoror different network operators. In some embodiments, the first andsecond cells are the same cell when the first and second cellscorrespond to two different numbers of the same network operator.Moreover, the Baseband chip 110 may read data from one of the subscriberidentity cards 160 and 170 via the dual SIM controller 130, and also maywrite data to one of the subscriber identity cards 160 and 170 via thedual SIM controller 130.

FIG. 2 shows a schematic diagram of a mobile station according to anembodiment of the invention. A dual SIM controller 220 iscoupled/connected between a Baseband chip 210 and two subscriberidentity cards 240 and 250, and the dual SIM controller 220 is poweredby the supplied voltages VBATT and VDD. The dual SIM controller 220comprises a serial peripheral interface (SPI I/F) 221, a control unit222, a switching circuit 223, two level shifters 224 and 226, and tworegulators 225 and 227, wherein the switching circuit 223 comprisesthree switching units CLK_SW, RST_SW and DAT_SW. In an embodiment, eachof the two regulators 225 and 227 may be a low dropout (LDO) regulator.The regulator 225 provides a voltage VCCA to the subscriber identitycard 240 as an operating voltage of the subscriber identity card 240,and the regulator 227 provides a voltage VCCB to the subscriber identitycard 250 as an operating voltage of the subscriber identity card 250.Moreover, a PMIC 230 generates a reset signal RESET to the Baseband chip210 and the control unit 222 after the mobile station is powered-on.

Referring to FIG. 2, the Baseband chip 210 comprises a SIM interface 212and a SPI I/F 214. The SIM interface 212 is coupled/connected to theswitching circuit 223, and the relative signals between each of the twosubscriber identity cards 240 and 250 and Baseband chip 210 aretransmitted via the SIM interface 212. The SPI I/F 214 iscoupled/connected to the SPI I/F 221, and the instructions from theBaseband chip 210 are transmitted to the control unit 222 via the SPII/Fs 214 and 221, which comprise the CS, SCK, SDI and SDO ports.

Moreover, the level shifter 224 and the LDO 225 are coupled/connected tothe subscriber identity card 240 which is used to camp on a cell (ex. afirst cell) via an RF module 260, and the level shifter 226 and the LDO227 are coupled/connected to the subscriber identity card 250 which isused to camp on another cell (ex. a second cell) via the RF module 260.The subscriber identity card 240 is coupled to the switching circuit 223via the level shifter 224, which may shift the relative signals betweenthe subscriber identity card 240 and the Baseband chip 210 to thesuitable voltage levels. Furthermore, the subscriber identity card 250is coupled to the switching circuit 223 via the level shifter 226, whichmay shift the relative signals between the subscriber identity card 250and the Baseband chip 210 to the suitable voltage levels. When receivingan instruction indicating that the subscriber identity card 240 or thesubscriber identity card 250 has been selected via the SPI I/Fs 214 and221, the control unit 222 controls the switching circuit 223 tocouple/connect the SIM I/F 212 to the selected subscriber identity cardfor enabling communication (such as the relative signals transmission)between the Baseband chip 210 and the selected subscriber identity cardvia the dual SIM controller 220. In this embodiment, the relativesignals comprise the data signals (ex. SIMDATA, DATA and DATB), resetsignals (ex. SIMRST, RSTA and RSTB) and clock signals (ex. SIMCLK, CLKAand CLKB).

For the inserted subscriber identity cards may operate with differentvoltage levels, the mobile station detects an operating voltage of eachinserted subscriber identity card and sets an operating voltage level ofeach level shifter and LDO to initiate the inserted subscriber identitycards after being powered-on. Referring to FIGS. 3A and 3B, anembodiment of a method for initiating operating voltages for subscriberidentity cards of a mobile station is provided. Referring to FIG. 2,FIG. 3A and FIG. 3B together, assume each of the inserted subscriberidentity cards 240 and 250 is operated with one of two voltage levels,for example, 3.0V and 1.8V. After being powered-on, the PMIC 230generates the reset signal to the Baseband unit 210. Next, the Basebandunit 210 generates a first signal indicating start of operating voltagedetection of the subscriber identity card 240 according to the resetsignal (step S302), wherein the first signal is received by the controlunit 222 of the dual SIM controller 220 via an interface between theBaseband unit 210 and the dual SIM controller 220. In an embodiment, theinterface between the Baseband unit 210 and the dual SIM controller 220is a Serial Peripheral Interface (SPI I/F). In another embodiment, theinterface may be a general purpose input/output (GPIO) or a universalasynchronous receiver/transmitter (UART) interface or the like. Thecontrol unit 222 subsequently controls the switching circuit 223 tocouple/connect the SIM I/F 212 of the Baseband unit 210 (such asterminals for outputting/inputting SIMCLK, SIMRST and SIMDATA signals)to the level shifter 224 (step S304), and directs the LDO 225 togenerate a voltage variable signal to the subscriber identity card 240(step S306). The voltage variable signal is an analog signal with afirst voltage level during a first time period and a second voltagelevel during a second time period. Refer to FIG. 4A, 4B, 4C or 4D forthe waveform illustrating voltage level variations, where v1 and v2represent the first and second voltage levels, respectively, and t1 andt2 represent the first and second time periods, respectively. In someembodiments, v1 may be 3V and v2 may be 1.8V shown in FIG. 4A or 4C. Insome embodiments, v1 may be 1.8V and v2 may be 3V shown in FIG. 4B or4D. During the first or second time period, when the voltage level ofthe voltage variable signal from the LDO 225 matches the operatingvoltage of the subscriber identity card 240, the subscriber identitycard 240 transmits a code indicating that its operating voltage matchesthe voltage of the voltage variable signal to the Baseband unit 210 viathe SIM interface 212 and the dual SIM controller 220 (step S308) suchthat the Baseband unit 210 can determine the operating voltage of thesubscriber identity card 240. For an example of the subscriber identitycard 240 operating at a voltage level of v2 shown in FIG. 4A, 4B, 4C or4D, during the second time period, the subscriber identity card 240transmits a code indicating that its operating voltage matches thevoltage of the voltage variable signal to the Baseband unit 210.According to the received code, the Baseband unit 210 generates asetting signal indicating that the operating voltage of the subscriberidentity card 240 is the first or second voltage level to the controlunit 222 via the SPI I/F (step S310). Next, the control unit 222 setsthe level shifter 224 and the LDO 225 to the indicted voltage level(i.e. the first or second voltage level) according to the setting signalfrom the Baseband unit 210 (step S312). After the voltage level settingsof the level shifter 224 and the LDO 225 are performed, the suitableoperating voltage is provided to the subscriber identity card 240 suchthat the subscriber identity card 240 can operate with the Baseband unit210 to camp on the first cell and communicate with a corresponding node(CN) via the camped on cell.

After detecting and setting the operating voltage of the subscriberidentity card 240, the Baseband unit 210 generates a second signalindicating start of operating voltage detection of the subscriberidentity card 250 (step S314), wherein the second signal is received bythe control unit 222 via the SPI FF. Next, the control unit 222 controlsthe switching circuit 223 to couple/connect the SIM I/F 212 to the levelshifter 226 (step S316), and directs the LDO 227 to generate the voltagevariable signal to the subscriber identity card 250 (step S318). Next,the Baseband unit 210 receives a code from the subscriber identity card250 via the SIM interface 212 and the dual SIM controller 220 when thevoltage variable signal is asserted and the voltage level of the voltagevariable signal from the LDO 227 matches the operating voltage of thesubscriber identity card 250 (step S320), wherein the code indicatesthat the operating voltage of the subscriber identity card 250 matchesthe voltage of the voltage variable signal. For an example of thesubscriber identity card 250 operating at a voltage level of v1 shown inFIG. 4A, 4B, 4C or 4D, during the first time period, the subscriberidentity card 250 transmits a code indicating that its operating voltagematches the voltage of the voltage variable signal to the Baseband unit210. According to the received code, the Baseband unit 210 generates asetting signal indicating that the operating voltage of the subscriberidentity card 250 is the first or second voltage level to the controlunit 222 via the SPI I/F (step S322). Next, the control unit 222 setsthe level shifter 226 and the LDO 227 to the indicted voltage levelaccording to the setting signal (step S324). After the voltage levelsettings of the level shifter 226 and the LDO 227 are performed, thesuitable operating voltage is provided to the subscriber identity card250 such that the subscriber identity card 250 can operate with theBaseband unit 210 to camp on the second cell and communicate with an CNvia the camped on cell.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. Those who are skilled in this technology can still makevarious alterations and modifications without departing from the scopeand spirit of this invention. Therefore, the scope of the presentinvention shall be defined and protected by the following claims andtheir equivalents.

1. A system for operating at least two subscriber identity cards,comprising: a subscriber identity module (SIM) controller, after beingpower-on, generating a first voltage variable signal with a firstvoltage level to a first subscriber identity card during a first timeperiod, generating the first voltage variable signal at a second voltagelevel to the first subscriber identity card during a second time period,receiving a first code indicating that generated voltage matches fromthe first subscriber identity card during the first or second timeperiod, generating a first operating voltage with the first voltagelevel to the first subscriber identity card when receiving the firstcode in the first time period, generating the first operating voltagewith the second voltage level when receiving the first code in thesecond time period, generating a second voltage variable signal with thefirst voltage level to a second subscriber identity card during a thirdtime period, generating the second voltage variable signal with thesecond voltage level to the second subscriber identity card during afourth time period, receiving a second code indicating that generatedvoltage matches from the second subscriber identity card during thethird or fourth time period, generating a second operating voltage withthe first voltage level to the second subscriber identity card whenreceiving the second code in the third time period, and generating thesecond operating voltage with the second voltage level to the secondsubscriber identity when receiving the second code in the fourth timeperiod, thereby enabling the first subscriber identity card and thesecond subscriber identity card to be operated at the first voltagelevel and the second voltage level respectively.
 2. The system asclaimed in claim 1, wherein the SIM controller further comprises: afirst regulator generating the first voltage variable signal withdifferent voltage levels in different time periods to the firstsubscriber identity card, and generating the first operating voltagewith one of the first voltage level and the second voltage level to thefirst subscriber identity card; and a second regulator generating thesecond voltage variable signal with different voltage levels indifferent time periods to the second subscriber identity card, andgenerating the second operating voltage with one of the first voltagelevel and the second voltage level to the second subscriber identitycard.
 3. The system as claimed in claim 2, wherein the SIM controllerfurther comprises a control unit directing the first regulator togenerate the first voltage variable signal with different voltage levelsin different time periods to the first subscriber identity card,directing the first regulator to generate the first operating voltagewith one of the first and second voltage levels according to receivingtime period of the first code, directing the second regulator togenerate the second voltage variable signal with different voltagelevels in different time periods to the second subscriber identity card,and directing the second regulator to generate the second operatingvoltage with one of the first and second voltage levels according toreceiving time period of the second code.
 4. The system as claimed inclaim 1, wherein the SIM controller further couples or connects ainterface to the first subscriber identity card before generating thefirst voltage variable signal to the first subscriber identity card,receives the first code via the interface after coupling or connectingthe interface to the first subscriber identity card, switchingly couplesor connects the interface to the second subscriber identity card aftergenerating the first operating voltage and before generating the secondvoltage variable signal to the second subscriber identity card, andreceives the second code via the interface after coupling or connectingthe interface to the subscriber identity card.
 5. The system as claimedin claim 4, wherein the interface is SIM interfaces.
 6. The system asclaimed in claim 4, wherein the SIM controller further determinesvoltage level of the first operating voltage according to a firstsetting signal from a Baseband unit, and determines voltage level of thesecond operating voltage according to a second setting signal from theBaseband unit.
 7. The system as claimed in claim 6, wherein the firstsetting signal and the second setting signal are transmitted from theBaseband unit to the controller via a serial peripheral interface (SPI)interface.
 8. The system as claimed in claim 4, wherein the SIMcontroller further comprises: a first level shifter; a second levelshifter; a switching circuit; and a control unit directing the switchingcircuit to couple or connect the interface to the first subscriberidentity card via the first level shifter before generating the firstvoltage variable signal to the first subscriber identity card, anddirecting the switching circuit to couple or connect the interface tothe second subscriber identity card via the second level shifter beforegenerating the second voltage variable signal to the second subscriberidentity card.
 9. The system as claimed in claim 1, wherein the SIMcontroller further reads out a first international mobile subscriberidentity (IMSI) from the first subscriber identity card for subsequentlysending to cellular network after successfully determining andgenerating voltage level of the first operating voltage, and reads out asecond IMSI from the second subscriber identity card for subsequentlysending to cellular network after successfully determining andgenerating voltage level of the second operating voltage.
 10. Asubscriber identity module (SIM) controller, comprising: a control unit;a first regulator, directed by the control unit, generating a firstvoltage variable signal with a first voltage level to a first subscriberidentity card during a first time period, and with a second voltagelevel to the first subscriber identity card during a second time period,and generating a first operating voltage with the first or secondvoltage level to the first subscriber identity card in response to whichtime period a first code indicating that generated voltage matches isreceived from the first subscriber identity card; and a secondregulator, directed by the control unit, generating a second voltagevariable signal with the first voltage level to a second subscriberidentity card during a third time period, and with the second voltagelevel to the second subscriber identity card during a fourth timeperiod, and generating a second operating voltage with the first orsecond voltage level to the second subscriber identity card in responseto which time period a second code indicating that generated voltagematches is received from the second subscriber identity card.
 11. TheSIM controller as claimed in claim 10, further comprising: a first levelshifter; a second level shifter; and a switching circuit, directed bythe control unit, coupling or connecting a interface to the firstsubscriber identity card via the first level shifter before generatingthe first voltage variable signal to the first subscriber identity card,such that the first code can be passed through the first level shifterto a Baseband unit, and switchingly coupling or connecting the interfaceto the second subscriber identity card via the second level shifterbefore generating the second voltage variable signal to the secondsubscriber identity card, such that the second code can be passedthrough the second level shifter to the Baseband unit.
 12. The SIMcontroller as claimed in claim 11, wherein the interface is SIMinterface.